Moisture measuring and control apparatus

ABSTRACT

An apparatus for measuring the moisture content of material being conveyed through a machine for conditioning the material to achieve a selected moisture content, and for controlling the speed at which the material is conveyed through the machine in order to subject the material to longer or shorter periods of exposure to the conditioner for the purpose of achieving the selected moisture content for the material. The apparatus includes: a moisture meter for measuring the moisture content of the material and producing an electric voltage signal which is related to the moisture content of the material, a reference signal generator which produces a reference voltage which is related to a selected moisture standard, a comparator which compares the measured moisture signal with the standard moisture signal and generates a dry condition signal when the measured moisture content is less than the standard moisture content by a predetermined amount and generates a wet condition signal when the measured moisture content exceeds the standard moisture content by a predetermined amount. Controls are provided which respond to the dry and wet condition signals in order to increase the speed or decrease the speed at which the material is conveyed through the machine. Timers are provided by which the dry and wet condition signals are prevented from actuating the speed controls except after a start time delay sufficient to permit the material in the machine when the machine is started to clear the machine, and a correction time delay which insures that a condition requiring correction persists long enough to warrant correction. An amount of correction timer is actuated after the time delays which unblocks the controls and permits them to respond to the dry and wet condition signals for a predetermined time period. A frequency of correction timer is provided which is actuated at the end of the time period established by the amount of correction timer to recycle the amount of correction timer at reoccurring intervals of predetermined frequency. The timers are all connected to a common power source and are energized in sequence by plural series connected switches. A wet stop control is provided to shut down the machine in case an excessive moisture condition is measured which cannot properly be corrected by the automatic controls.

United States Patent 1 m1 Strandberg, Jr. et al. 51

3,732,435 May 8, 1973 [54] MOISTURE MEASURING AND CONTROL APPARATUS [75]Inventors: Charles F. Strandberg, Jr.; Robert C. Strandberg, both ofGreensboro, NC.

the selected moisture content for the material. The apparatus includes:a moisture meter for measuring the moisture content of the material andproducing an electric voltage signal which is related to the moisturecontent of the material, a reference signal generator which produces areference voltage which is related to a selected moisture standard, acomparator which compares the measured moisture signal with the standardmoisture signal and generates a dry condition signal when the measuredmoisture content is less than the standard moisture content by apredetermined amount and generates a wet condition signal when themeasured moisture content exceeds the standard [73] Assignee: StrandbergEngineering Laboratories, Inc., Greensboro, NC.

[22] Filed: Mar. 27, 1972 [21] Appl. No.: 238,114

moisture content a redetermined amount Con- [51] Int. Cl ..F26b 13/12trols are provided which respond to the dry and wet [58] Field Of Search..34/43, 52; 307/118; condition ignals in order to ine 'ease the speed o32 /65 decrease the speed at which the material is conveyed through themachine. Timers are provided by which [56] References Cited the dry andwet condition signals are prevented from actuating the speed controlsexcept after a start time delay sufficient to permit the material in themachine when the machine is started to clear the machine, and

UNITED STATES PATENTS 2,702,948 3 1955 Seney ..34 s2 2,942,352 6/1960Eicken-Estienne ..34 52 a correctlon delay Winch msures that a Commonrequiring correction persists long enough to warrant FOREGN PATENTS 0RAPPLICATIONS QQEKE9BAH3KQJLQEQfiSQiWQfiQEJEHEEw fiqy 1,102,062 1/1965Great Britain ..307/l 18 after the delays whch blocks 93 commls and -2Primary Examiner--Robert K. Schaefer Assistant Examiner-William J. Smith'nEmitsYheTnTrTmWfil to the dry and wet condition signals for apredetermined time period. A frequency of correction timer is providedwhich is actuated at the end of the time period established by theamount Att0mey Munson Lane et of correction timer to recycle the amountof cor- An apparatus for measuring the moisture content of materialbeing conveyed through a machine for conditioning the material toachieve a selected moisture content, and for controlling the speed atwhich the material conveyed through the machine in orderto bi t w netaShefiiiiidafs;

posureto theconditioner for the purpose of achieving ABSTRACT 20(Ilaims, 8 Drawing Figures -v3 r58 wET oouTRoI. f STOP SENSITIVITY DRYCONTROL sELEcToR CORRECTION '6 l8 RELAY 24 areas: t MOISTURE REVERSIBLE46 CONTROL xI RI4 CORRECTION MEASURING COMPARATOR x2 Rl3 R|5 l MEANSMOTOR MATERIAL j 02 2| WET I MOTOR co NT Ro L CORRECTlON SPEED POINT V vI RELAY -23 CONTROL sELEcToR I vARIAaLE 1 L26 LI? 138 25 1 SPEED DRIvEMOTOR i-" RUN RELAY CONTACTS OPEN m sToPa sLow CLOSED IN RUN 0a 33 QI932 u r A L START coRR. FREQ. or DELAY DELAY YYET OR DRY CORR D57 1 msR27 R TWER MI 901 R28 sELEcToR R52 c4 sTART c6 coRREcT Auouur OF TFREQUENCY or I DELAY I CORRECTION RESET l CORRECTION TIMER TIMER TIMERcIo TIMER 4 2, 29 30 LY .L

t T T T PATENT-EUHAY 819 75 HEET 5 0F 5 FIG-'6.

MOISTURE MEASURING AND CONTROL APPARATUS The invention relates to animproved continuous type moisture measuring and controlling instrumentfor measuring the moisture content of material treated in a moistureconditioning machine and for controlling the machine speed so as to holdthe moisture in the finished product relatively constant.

One particular moisture conditioning machine with which the invention isadapted is a web dryer having variable speed conveying means for movingthe web through the dryer. The invention measures the moisture contentof the web having the drier, compares the measured moisture content witha selected moisture standard and controls the speed of the conveyingmeans moving the web in response to signals in dicating the deviation ofthe measured moisture content from the selected standard moisturecontent by predetermined amounts. The controls decrease the speed of theweb conveying means when the web condition is too wet and increase thespeed of the web conveying means when the web is too dry.

It is an object of this invention to provide improved control means forcorrecting abnormal moisture conditions in the web without excessivehunting so as to hold the moisture in the finished product relativelyconstant.

It is another object of the invention to provide improved timing meansfor permitting the controls to respond to dry and wet correction signals(obtained by comparing a measured material moisture content with aselected standard material moisture content) only during periods ofpredetermined time duration at reoccurring intervals of predeterminedfrequency and only after a time delay period.

It is an object of the invention to include a start delay timer forestablishing a start time delay period sufficient to allow material inthe conditioning machine at the time it is started to clear the machine,a correction delay timer for establishing a correction delay periodsufficient to ascertain that the abnormal moisture condition persistslong enough to warrant corrective action, an amount of correction timerfor establishing the time period during which the controls are permittedto take corrective action, and a frequency of correction timer which isenergized at the end of the time period established by the amount ofcorrection timer to prevent the controls from making anotherspeedcorrection until sufficient time has elapsed to allow the initialspeed correction to influence the moisture. The frequency of correctiontimer resets the amount of correction timer after a predetermined timeperiod and continues to operate alternately with the amount ofcorrection timer as long as the machine is running and abnormal moisturesignals are being produced. When the measured moisture condition returnsto within a normal moisture condition zone centered with respect to aselected standard moisture condition, all of the timers except the startdelay timer will be deenergized and put in readiness to begin a newtiming interval upon the reoccurrance of persisting abnormal moisturecondition signals.

It is another object of this invention to provide an amount ofcorrection timer which includes separate timing circuits, one a drycorrection timing circuit for timing a dry correction period, and theother a wet correction timing circuit for timing a wet correctionperiod, and means for selecting which timer is operative in accordancewith whether a wet or dry abnormal moisture condition signal is beinggenerated. The separate timing circuits are provided so that the amountof wet correction time may be selected to be longer than the amount ofdry correction time in order to better assure adequate drying.

It is another object of the invention to connect the start delay timer,the correction delay timer, the amount of correction timer, and thefrequency of correction timer so that they may be energized in sequencewhen the conditioning machine is put in run condition. The timers arepreferably solid state devices and solid state switches are preferablyprovide between the respective timers in series circuit with a powersource, which switches control the sequence of operation of the timers.

It is another object of the invention to provide a wet stop controlwhich will shut down the moisture conditioning machine when an excessivewet moisture condition occurs.

With the foregoing objects and features in view and such other objectsand features which may become apparent as this specification proceedsthe invention will be understood from the following description taken inconjunction with the accompanying drawings, wherein like characters ofreference designate like parts and wherein:

FIG. 1 is a partial block and partial schematic diagram showing theinvention as adapted for one particular use;

FIGS. 2A, 2B and 2C are schematic diagrams of sections of the inventionand when put together with FIG. 2A above and FIGS. 28 and 2C positionedin horizontal alignment below FIG. 2A, they together form the completeschematic diagram of the invention;

FIG. 3 is an elevational view showing the front control and displaypanel provided on the main housing for the invention;

FIG. 4 is a perspective view showing a knurled detector roll forming acomponent of the invention;'-

FIG. 5 is a perspective view showing a detector roll which is smoothsurfaced forming an alternate com- I ponent of the invention, and

FIG. 6 is a perspective view showing a spiked detector roll forminganother alternate component of the invention.

Referring now to the accompanying drawings and to FIG. 1 in particular,the invention 10 is illustrated as adapted to one particular use forcontinuously measuring the moisture content of web material 13 after itpasses through a material conditioning means 11, such as a dryer, andfor controlling the speed of a variable speed drive means 14, such as avariable speed electric motor, which drives the material conveyor means15. Measuring means 16 is provided for continuously measuring themoisture content of the material and for producing an electrical outputsignal which is related to the moisture content of the material. Acontrol point selector means 17 is provided for generating a referencesignal related to a standard moisture content desired for the materialbeing treated. The measured moisture content signal from the moisturemeasuring means is compared with the selected standard moisture signalfrom the control point selector 17 in a control comparator means 18. Thecontrol comparator means 18 has two output channels 20 and 21 which maybe designated a dry condition signal channel, and a wet condition signalchannel respectively. The control comparator means generates a normalcondition signal when the measured moisture content is within apredetermined range centered with respect to the selected standardmoisture content. The normal signal comprises like and equal outputs inchannels 20 and 21. The control comparator means 18 generates a wetcondition signal when the measured moisture content exceeds the standardmoisture content by a predetermined amount, and it generates a drycondition signal when the measured moisture content is less than thestandard moisture content by a predetermined amount. A controlsensitivity selector which provides means for adjusting the comparatorto determine the limits of the predetermined range by which the measuredmoisture content may vary from the standard moisture content so that thecomparator means will produce a normal signal is designated at 19. Thedry signal condition channel 20, including a resistor R12 is connectedto the base of transistor Q1 which provides means responsive to the drycondition signal for producing dry correction control signals. Thetransistor Q1 is connected between ground and the negative side of agrounded voltage source V3 in series with the energizing coil of a drycorrection relay 22. The wet condition signal channel 21, including aresistor R13 is connected to the base of transistor Q2 which providesmeans responsive to the wet condition signal for producing wetcorrection control signals. The transistor Q2 is connected betweenground and the negative side of a grounded voltage source V3 in serieswith the energizing coil of a wet correction relay 23. The transistorsQ1 and Q2 function like normally open switches which are responsive todry or wet condition signals respectively for closing. Closing of theswitch Q1 energizes the dry correction relay 22 while closing of theswitch Q2 energizes the wet correction relay 23. The dry correctionrelay 22 and the wet correction relay 23 have contacts in a reversingcircuit supplying energy to the reversible correction control motor 24which is suitably connected by drive means 25 to adjust speed controlmeans 26 for controlling the variable speed drive means 14. When the drycorrection relay 22 is energized the reversible correction control motoris rotated in a direction which adjusts the speed control means 26 toincrease the speed of the variable speed drive means 14, and when thewet correction relay 23 is energized the reversible correction controlmotor is rotated in a direction which adjusts the speed control means 26to decrease the speed of the variable speed drive means 14.

While the invention as described thus far has been describedparticularly with application to drying web material it should berecognized that the invention is adaptable for providing other moistureconditioning functions for the material. For example, the materialconditioning means could conceivably be means for adding moisture to thematerial being treated, in which case a dry condition signal wouldindicate that the material should remain in the conditioning means for alonger time, and a wet condition signal would indicate that the materialshould remain in the conditioning means for a shorter period. It wouldthus be necessary to connect the reversible control motor so that a drycorrection control signal would cause the reversible control motor tomove in a direction to adjust the motor speed control to decrease thespeed of the variable speed drive means, and a wet correction controlsignal would cause the reversible control motor to move in a directionto adjust the motor speed control to increase the speed of the variablespeed drive means.

The system so far described with respect to FIG. 1 if used by itselfwould produce undesired hunting by the correction control motor. Inorder to improve the system response the invention includes timing meansgenerally indicated by the reference numeral 27 in the bottom half ofFIG. 1. The timing means 27 permits the transistors Q1 and O2 to respondto dry and wet condition signals respectively only during periods ofpredetermined time duration at reoccurring intervals of predeterminedfrequency while the dry or wet condition signals as the case may becontinue to be generated by the comparator 18 and only after a timedelay period initiated when the moisture conditioning means begins torun at normal speed.

The timing means 27 includes a start delay timer means 28, a correctiondelay timer means 29, an amount of correction delay timer means 30 and afrequency of correction timer 31 which are connected in parallel with adc. voltage source V2 at spaced intervals along the line 32 in the ordernamed from the positive side of V2 toward ground 34. The conducting line32 includes a plurality of switches 33, Q8, Q12 and Q19, and anindicator lamp DS7. The switch 33 is actuated by the run relay or otherswitch means which turns on the material conveyor drive motor. Theswitch 33 is positioned between the positive side of V2 and the startdelay timer 28. The switches Q8, Q12 and Q19 are solid state switches.O8 is positioned between the start delay timer 28 and the correctiondelay timer 29, Q12 is positioned between the correction delay timer 29and the amount of correction timer 30, and Q19 is positioned between theamount of correction timer 30 and the frequency of correction timer 31.

The start delay timer begins its timing cycle when the switch 33 isclosed. After a predetermined time period which may be adjusted by thestart delay potentiometer R16, the start delay timer will close theswitch Q8 provided a wet or dry condition signal is present on the line35 taken from the common junction between oppositely directed diodes X1and X2 which are connected to the dry condition channel 20 and the wetcondition channel 21 respectively. The time delay for which the startdelay timer is adjusted is the time required to allow all the drymaterial in the dryer at the time the dryer is started to be deliveredout of the dryer. If an abnormal (dry or wet) condition signal ispresent on the line 35 at the end of the start time delay period theswitch Q8 will close and the correction delay timer 29 will be energizedto begin a correction time delay period which is provided to assure thatthe abnormal moisture condition persists long enough to warrant action.The correction delay timer is initiated each time the control comparatorsenses an abnormal condition. The correction delay timer is adjustablefor different time delay periods by means of the correction delaypotentiometer R28.

At the end of the correction delay period the correction delay timercloses the transistor switch Q12 and the amount of correction timer 30is energized to initiate an amount of correction time period. As will besubsequently explained in more detail the amount of correction timer 30is actually two timers, a wet correction timer and a dry correctiontimer which are selectively actuated by a wet or dry timer selectormeans 36. The wet correction timer is normally selected by the selectormeans 36 unless a dry signal appears on the control line 37 connectedbetween the dry condition signal channel 20 and the wet or dry selectormeans 36 in which event the dry correction timer will be selected. Thewet correction timer is set for a longer time period than the drycorrection timer to better assure adequate drying of the web material13.

The amount of correction timer 30 normally provides a hold off biasvoltage on the line 38 connected between the amount of correction timerand the common junction 39 between resistors R14 and R15 which areconnected to the dry condition channel and the wet condition channel 21respectively. The hold off bias voltage on line 38 is sufficient toprevent a dry condition signal on channel 20 from closing the transistorswitch Q1 and to prevent a wet condition signal on channel 21 fromclosing the transistor switch Q2. However, during the time that theamount of correction timer is timing a correction time period, which maybe either a dry or wet correction, the hold off bias voltage is removedfrom the line 38 permitting Q1 and Q2 to respond to abnormal conditionsignals appearing in channels 20 and 21 respectively.

At the end of the amount of correction time period the hold off voltageis again applied to the line 38 to open the switches Q1 and Q2 dependingon which one is not already open. Also at the end of the amount ofcorrection time period the timer 30 closes the transistor switch Q19thus energizing the frequency of correction timer 31. When the switchQ19 is closed a bias voltage is applied through control line 41 toprevent the amount of correction timer from beginning a new cycle. Thefrequency of correction timer once energized times for a predeterminedperiod selected by the setting of the frequency of correctionpotentiometer R52. When the time interval of the frequency of correctiontimer 31 ends an output reset pulse is fed over the reset line 40 to theamount of correction timer 30. The reset pulse over line 40 causes thetransistor switch Q19 to open and the amount of correction timer tobegin a new timing cycle. The alternate operation of the amount ofcorrection timer 30 and the frequency of correction timer 31 willcontinue as long as abnormal signals (wet or dry) are generated by thecontrol comparator 18 and for as long as the material conveying andconditioning machinery remains in run. When the measured moisturecontent of the material returns to the normal zone the switch Q8 willopen and the correction delay timer, the amount of correction timer andthe frequency of correction timer will all be de-energized. When themeasured moisture content once again deviates from the normal zone eachof these timers will again be energized in sequence to again provide thenecessary operation of the correction control motor to effect thenecessary compensation in the speed of the variable speed drive means toachieve the desired moisture content in the material 13.

CIRCUIT ANALYSIS FIGS. 2A, 2B and 2C show the complete electricalschematic of the invention with the exception of power supplies,switches, and terminal strips. Aside from the a.c. voltage required foroperation of the reversible two-phase correction control motor 24, thecircuit operates from three independent regulated d.c. supplies, Vl, +V2and V3. Typical values for these supplies are Vl (lSOV), +V2 (+12V), and-V3 (+12V).

The circuit elements, shown as triangles on the schematic and labeled1C1, 1C2 and 1C3 are general purpose, integrated circuit, operationalamplifiers. No specific type is required. A suitable device, utilized inthe instrument is a UA741, manufactured by Fairchild Semiconductor.

The circuit elements, labeled Q3, Q9, Q15 and Q20 are programmableunijunction transistors, such as 2N6028, manufactured by GeneralElectric Co.

All other circuit elements are readily identifiable from their symbolsand no specific types are required.

The schematic is broadly sub-divided into major circuit functions forclarity. The theory of operation of each is described below.

The moisture to current converter provides means for sensing themoisture in the web and converting the resistance characteristic,inversely related to the moisture, into a meaningful electrical signal.With the detector roll 12 contacting the web 13 directly opposite thegrounded machine roll 9, the resistance of the web is directly in serieswith the set moisture control R1 from ground to VI. The vacuum tube 42is connected as a cathode-follower to provide a very highinput-impedance voltage measurement of the voltage drop across R1, whichis directly related to the moisture in the web. As the moisture in theweb 13 increases, the resistance decreases. Therefore, the voltage dropacross R1 increases. Conversely, as the moisture in the web decreases,the resistance of the web increases and the voltage drop across R1decreases.

The value of the set moisture control R1 can be varied to allow forcalibration of the instrument for different web materials. Generally thevalue of R1 is set to be equivalent to the resistance of the web at thedesired moisture level.

The voltage drop across R1 causes a proportional current to flow throughthe tube 42. The plate of vacuum tube 42 is connected directly to theinverting input of ICl. This point is a virtual ground since it is thesumming node for the amplifier.

' The current to voltage converter and indicator is a standard invertingamplifier used to convert and properly scale the current from the vacuumtube 42 into a ground-referred voltage'for operation of the indicatingmeter M1 and subsequent control circuits. Resistor R4 determines theoutput voltage of 1C1 and capacitor C2 provides the required damping forboth the indicator M1 and control circuits.

The control comparator 18 consists of two operational amplifiersoperating open loop for maximum sensitivity. A reference voltage is seton the control point control R7. This voltage is connected to theinverting input of lC2 and to the non-inverting input of 1C3. The outputof 1C1 is connected in reverse manner to the non-inverting input of 1C2and to the inverting input of [C3.

To provide a center-scale dead zone (normal), a separate controlsensitivity control R6 is included. This control provides means forcalibrating the control circuitry to the limits of the green, normalzone on the indicating meter.

Once properly calibrated, the output of both 1C2 and IC3 will bepositive so long as the meter indication remains in the normal zone.Should the meter indication fall into the dry zone, the output of [C2will go negative. In similar manner, should the meter indication riseinto the wet zone, the output of [C3 will go negative. Subsequentoperation of the dry correction relay 22 or the wet correction relay 23is conditional upon the status of the various timers in the timing means2f7.

Prior to describing the operation of each of the timers it is to bepointed out that the power supply connection to all of the timercircuitry is via the run relay contacts 33. This is a spare set ofnormally open run relay contacts on the machine. Only when the machineis placed in the run position will these contacts close, therebyproviding power from .-l-V2 to the timers. Also, note that transistorQ17, in the amount of correction timer, is connected, via R49 at alltimes to +V2. Therefore at any time that Q17 is off, a positive voltagewill be applied via resistors R14 and R15 to the bases of transistors Q1and Q2, respectively. This positive signal is of sufficient magnitude tooveride any negative signal from the outputs of [C2 and 1C3.Consequently it is necessary that transistor Q17 be on before anyoperation of either the dry correction relay 22 or wet correction relay23 is possible. Also note that transistor Q13 is connected via R37 tothe output of 1C2. At any time that the output of [C2 goes negative(meter indication in the dry zone), Q13 will turn on, thereby energizingrelay K3. The two sets of contacts of K3 are connected to select eitherpotentiometer R39 or potentiometer R40 and also either lamp D85 or lampDS6. This permits one amount of correction timer circuit to actuallyprovide two separate timing functions amount of dry correction and.amount of wet correction. The lamps D85 and D86, as well as lamps DS3,D84 and D87 simply serve to identify which timer is on.

Each of the four timers is basically the same. However additionaltransistors have been added to certain timers to provide appropriateinput or output control of each. Description of the basic timing meansof one will serve for all. All of the additional circuit elements willbe described in detail as to their particular function.

The start delay timer 28 is included to delay all correction control fora preset time after the machine has started. When the run relay contactsclose, capacitor C4 begins to charge via the start delay control R16.Resistors R18 and R19 set the intrinsic stand-off ratio of theprogrammable unijunction transistor Q3. Transistors Q4 and OS areconnected in a bi-stable arrangement so as to provide a continuousoutput after the start time delay. Simultaneously with the closure ofthe run relay contacts 33, Q turns on and Q4 remains off. Capacitor C5ensures that Q4 remains off long enough for O5 to turn on via base drivefrom R23. With OS on, Q4 will remain off until the start time delay hasexpired, then being turned on as C4 discharges through Q3 into R17. OnceQ4 turns on, Q5 will turn off and Q4 will remain on via base drive fromR22. Note that while the start delay timer 28 was in the timing state,with OS on, the lamp DS3 was on, thereby providing visual identificationthat the start delay timer was on.

Similar bi-stable circuits are employed in both the correction delaytimer 29 and the amount of correction timer 30. No such circuit isincluded in the frequency of correction timer 31 however. Since theamount of correction timer 30 and the frequency of correction timer 31operate together in tandem, the bi-stable circuit is not necessary inthe frequency of correction timer 31, and the output of the frequency ofcorrection timer, at the junction of Q20 and R53, is connected, via R50,back to the amount of correction timer 30 to reset its bi-stable circuitand, thereby re-start the amount of correction timer.

However prior to a detailed explanation of these two timers consideragain the start delay timer 28. After the start time delay has expired,no further timer operation will ensue until and unless either the outputof 1C2 or [C3 goes negative, indicating either a dry or wet condition onthe meter Ml. As long as the meter indication remains in the normalzone, the outputs of both 1C2 and 1C3 remain positive. Steering diodesX1 and X2 are reverse biased and block the positive signals. TransistorO6 is held on via base drive from R25. This effectively grounds the baseof Q7, holding it off. With Q7 off, 08 is off and since this transistoracts as a series switch for controlling the application of +V2 to theremaining timers, each of the three remaining timers is de-energized.

Now, assume that the output of 1C2 goes negative, indicating a drycondition on the meter M1. Diode X1 is now forward biased and thisnegative signal is fed, via R26 to the base of Q6. The magnitude of thissignal is sufficient to override the positive base drive from R25 and Q6turns off. With the base of Q7 now positive with respect to itseffectively grounded emitter (Q4 on), Q7 turns on thereby turning on,Q8and applying +V2 to the correction delay timer 29.

Operation of .the correction delay timeris identical to that of thestart delay timer 28. During the interval that the timer is timing, Q11is on, Q10 is off, and the next series switch Q12 is also off, blocking+V2 from the amount of correction timer 30 and the frequency'ofcorrection timer 31. When the correction delay ends, 010 turns on andQ11 turns off. With Q10 on, Q12 turns on and +V2 is now applied to theamount of correction timer 30.

Operation of the amount of correction timer 30 is also identical to thatof the previous timer except for the addition of Q14 and R38. Howeverduring the timing interval of the amount of correction timer 30, Q14 isoff since the next series switch Q19 is off. Therefore C8 is charged viathe amount of dry correction control R39 since the output of lC2 isnegative, thereby energizing K3. Transistor Q18 is on, D is on, Q16 isoff, and Q19 is off. With Q16 off, Q17 is turned on. This removes thepositive hold-off voltage from the base of Q1 and the negative outputfrom lC2 turns Q1 on via R12. The dry correction relay 22 is nowenergized and the correction control motor 24 rotates in the properdirection to affect an increase in the machine speed. When the amount ofdry correction time interval ends, Q16 turns on, Q17 turns off, and thepositive hold-off voltage is once again applied to the base of Q1 and Q1turns off, tie-energizing dry correction relay 22 and terminatingrotation of the correction control motor 24. Also when Q16 turns on, Q19turns on, applying +V2 to the frequency of correction timer 31. As thetimer 31 begins its timing interval, Q14 is turned on via R38. With 014now on C8 cannot be charged again via R39. This assures that the nexttiming interval of the amount of correction timer 30 is accurate.

When the time interval of the frequency of correction timer 31 ends, theoutput pulse from 020 via R50 causes Q18 to turn on, thereby removingthe base drive to Q16 via R46. As Q16 turns off, Q19 also turns off, Q14turns off, and another amount of dry correction time interval begins.This tandem operation of these two timers 30 and 31 will continue aslong as the meter M1 indication remains in the dry zone for as long asthe machine remains in run. When the meter M1 indication returns to thenormal zone, Q8 will turn off, and the correction delay timer 29, theamount of correction timer 30, and the frequency of correction timer 31will all be de-energized. When the meter M1 indication once againdeviates from the normal zone, each of these timers 29, 30 and 31 willagain be energized, in sequence, to again provide the necessaryoperation of the correction control motor 24 to affect the necessarycompensation in machine speed to achieve the desired moisture level seton the set moisture control R1.

While electronic timers and switches are described in the specificationand drawings, suitable electromechanical timers and various types ofswitches may be substituted which will perform the timing and switchingfunctions described and fall within the spirit and scope of theinvention as claimed.

Referring now to FIG. 3 the instrument housing 43 mounted on stand 45and provided with a front display and control panel 44 is shown. Thehousing 43 will normally contain all of the instrument components shownin FIGS. 2A, 2B and 2C with the exception'of the detector roll 12 andgrounded roll 9. The detector roll 12 is preferably located at thedelivery end of the material conditioner as near as possible to thepoint at which the web 13 is rolled or folded. If one detector roll isused, it should be mounted in the center of the web. If more than onedetector roll is used, they should be connected together. The detectorroll 12 is connected by high dielectric wire 46 to a junction 47 insideof the housing 43 between R1 and R2 in the moisture to current convertercircuit (see FIG. 2A). The correction control motor 24 and the speedcontrol potentiometer 26 are preferably housed in housing 43 but theymay be mounted externally in proximity to the variable speed drive motor14 for the material conveyor if desired. If the correction control motor24 and the speed control potentiometer 26' are mounted in housing 43suitable wiring connections are provided to connect the speed controlpotentiometer 26 in the speed control circuit for the variable speeddrive motor 14. The speed control for the variable speed drive motor 14is of conventional design for which reason it is shown only by block 26in FIG. 1. It will be understood that the speed control potentiometer26' is connected in the energizing circuits for the variable speed drivemotor 14 in such a way that varying the position of the potentiometermovable contact 26a will cause a variation in speed of the drive motor14.

On the front panel 44 is positioned the indicator dial 47a for themoisture meter M1. The indicator dial is divided into three zones ofmoisture condition: dry, normal and wet. The dry and wet zones, coloredred, indicate conditions that are abnormal. The center normal zone,colored green, indicates that the moisture in the material is normal. Itshould be mentioned at this point that the meter M1 may be a meter relaytype which is provided with a circuit contact 47' which when engaged bythe pointer 47" at the extreme end of the wet zone will operate a relayor other wet stop control 58 to shut down the moisture conditioningmachine. Such wet stop control 58 is desirable when the moisture contentof the material reaches a predetermined high level beyond which theconditioning machine and the controls therefor will not operatesatisfactorily. Instead of a meter relay other wet stop controls may beused. Another suitable wet stop control would include a wet stopcomparator and a wet stop control point selector like comparator 18 andcontrol point selector 17 which would be connected to the output of themoisture measuring means 16 in parallel with comparator 18. The wet stopset point selector would be set to a selected high moisture standardwhich if exceeded by the measured moisture content would cause the wetstop comparator to provide a signal which turns the moistureconditioning machine off.

Beneath the meter indicating dial 47a is a selector 48, marked SetRegain. The knob for selector 48 turns the set moisture resistor R1 inthe moisture meter circuit shown in FIG. 2A. The Set Regain selector iscalibrated in units from 3 to 15 which correspond directly to themoisture in cotton expressed as a percentage of its dry weight. Theunits also correspond in precisely known relationships to moisture inother natural and man-made fibers as well as to any blends of these. Tothe leftof the Set Regain selector is a power on-off switch 49 whichturns the moisture conditioning machine and the measuring and controlapparatus of this invention on and off. To'the right of the set regainselector is a mode selector switch control knob 50 which enables theoperator to put the machine speed control in manual or automatic. Whenin manual position the reversible correction control motor maybeactuated to increase machine speed by manually pressing the dry manualswitch button 56, or to decrease machine speed by pressing the wetmanual switch button 57. The contacts of the dry switch button 56 arepositioned across the contacts 22' of the dry correction relay 22 andthe contacts of the wet switch button are positioned across the contacts23' of the wet correction relay 23.

At the bottom of the panel 44 are selector knobs 51, 52, 53, 54 and 55which actuate the start delay potentiometer R16, the correction delaypotentiometer R28, the amount of dry correction potentiometer R39, theamount of wet correction potentiometer R40, and the frequency ofcorrection potentiometer R52, respectively. The dial for the start delayselector 51 is calibrated in minutes from 0 to 3.0, while the dials forthe remaining four selectors 52-55 are calibrated in seconds from to 60.Directly above the selector knobs 511-55 are indicator lamps DS3-DS7which when lighted indicate that their associated timer is timing.

MOISTURE SENSORS The moisture sensors used with this invention areelectric devices which sense the moisture content in the material beingtested and they are of different types depending on the type of moisturemeter being used, and the nature of the material being tested. For aresistance type moisture meter which passes an electric current throughthe material, and senses the variation of electric current inrelationship to the electrical resistance of the material and in turn asa function of moisture content, the moisture sensors are electricconductors in the form of rollers, bars and the like. When the moisturecontent of a fabric web is being sensed the moisture sensors arepreferably detector rolls as illustrated at 12 in FIGS. 1 and 2A of thedrawings. The detector rolls 12 may be selected as to weight and contactsurface for different materials.

For use with sizing machine, i.e., slashers, a single medium-weight roll12 is usually mounted over the nip roll 9 in the center of the warp atthe delivery end of the machine. Heavy detector rolls are needed onheavy yarn which may be damp. For yarn counts under 20 a heavy, knurledroll is recommended. Wet warps can result from using light-weight rollson heavy warps, because the moisture control will sense a dry surfaceand cause the machine speed to be increased. In these instances the warpsurface on the loom beam may even feel hot and dry. If the slasher isallowed to stand for a few minutes, the surface may become cold anddamp. Considerable warp losses have resulted from this condition,confusing both the moisture control and the operator.

Continuous filament yarns, such as Nylon, of low denier are susceptibleto damage from detector rolls. Special, light-weight rolls arerecommended for these applications to prevent the roll frompermanentlyflattening the yarn.

It is not advisable to locate detector rolls before the leasing sectionimmediately after drying. The reason for this is that the latent heatcontained in the yarn immediatelyafter drying. can cause rapid andcontinued drying as the yarn passes through the open and exposed'leasing section. This is generally true for all fibers, both natural andman-made, except at extremely low speeds. At these low speeds, it ispossible for overdried yarn to pickup moisture when it is exposed in theleasing section.

It is generally unnecessary to employ more than one centrally locateddetector roll on modern slashers. However, additional rolls can beemployed for the purpose of assuring even size pickup and moistureacross the warp. A selector position is available to combine all of therolls together. The moisture control will be influenced largely by thedetector roll which is in contact with the dampest part of the warp.

Full-span detectors, such as a pair of closely spaced rolls, can beemployed. Although this arrangement is seldom used, it offers theadvantage of permitting the wet stop device to respond to a few wet endsanywhere in the warp. The wet condition can result from lapped yarn ordents on one of the squeeze rolls. When fullspan detectors are used, itis recommended that a single short detector roll be located in thecenter of the warp to provide better control consistency. The twodetectors should be connected together.

The use of predryers in both dye-beam and doubledip systems brings abouta size pickup problem as a result of variations in the residual moisturein the yarn before it enters a size box. The moisture in dry yarn isvery consistent, so no significant variations in pickup result. Dampyarn emerging from a predryer will provide increased pickup due to itshigher moisture, but, if the moisture is variable, the pickup will bevariable.

Detector rolls can be located at the exits of predryers, and moisturecontrols can be employed to regulate the predryer temperature to obtainmore consistent moisture and more consistent size pickup.

Much of what has been said about the use of detector rolls on slashersalso applies to fabric dryers.

Single, medium-weight detector rolls are usually employed without regardto fabric density. The effects of size penetration experienced withsizing heavy yarns is generally not experienced on fabric, butlight-weight rolls may be necessary to avoid damage to hot fabrics.

it is generally advisable to locate detector rolls at the delivery endas near as possible to the point at which the fabric will be rolled orfolded. As in the case of slashers, considerable moisture evaporationcan occur in the threading section after drying as a result of thelatent heat contained in the fabric.

The effect of latent heat in fabric can be utilized in curing operationsby intentionally locating detector rolls at dryer exits. Although themoisture control will not ascertain the complete absence of moisture, itwill accurately ascertain extremely low levels of moisture. By settingthe moisture control for the lowest moisture level and by locating thedetector roll at the dryer exit, the complete absence of moisture cangenerally be assured at the entrance to the curing oven or section.Substantial increases in production can often be accomplished by thismethod.

Full-span detector rolls or bars are useful on multistrand dryers. Themoisture control will be influenced largely by the dampest strand.

Teflon insulated detector roll wire is recommended when detector rollsare located on very hot fabric or when they are installed inside dryers.I

' Spiked detector rolls are available for penetrating through the pileside of carpet tothe base. A pair of these rolls, one behind the other,can be employed. Smooth-surface rolls, can be used on the back side ofcarpet in the same manner.

A single or double probe is available for mounting inside the air ductof raw stock dryers. Although the probe may not consistently contact thestock as it moves through the duct, the moisture control will seek anaverage value of the contacts and can be used to control the apronspeed, the feed rate, or both.

Special detectors can be made for new or unusual applications. Theprimary requisites are contact consistency and high insulationresistance. Good insulation materials include Teflon, which is capableof withstanding very high temperatures, and polyvinylchloride (PVC),which performs well as an electrical insulator but is limited to use atfairly low temperatures.

FIGS. 4 to 6 are illustrative of different detector rolls 12, 12a and12b, which may be used with the invention. Detector roll 12 shown inFIG. is a smooth surface conductive roll, roll 120 (FIG. 4 is a knurledsurface conductive roll, and roll 12b is a spiked surface con ductiveroll. Each of the rolls have opposite shaft ends 63 (only one shown)which are journalled in bearings at the ends of the parallel arms of theconductive yoke 59. The yoke 59 is supported by a rearwardly extendinghandle 60, preferably insulated, to which support brackets 61 aresecured. The brackets 61 have aligned holes 65 through which a pivot pinmay be positioned for pivotally attaching the'handle 60 to a suitablesupport at the site where the detector roll is to be used. An insulatedconductor 46 which is electrically connected to the yoke 59 extends to aconnector 62 from which a cable connection may be made extending to themoisture measuring means 16 contained in the housing 43 (see FIG. 3).Conductive spacers 64 are provided between the ends of rolls 12, 12a and12b and the yokes if required to insure adequate conductive contactbetween the rolls and the arms of yoke 59.

CALIBRATION TIMER SETTINGS The start delay timer 28, adjustable from 0to 3 minutes, serves to disable the control during the time the dryer 11is standing or operating at low speed as well as for an adjustable,preset time after starting or returning to normal, run speed. Withoutthe start delay provided by the timer 28 the control would sense anexcessively dry condition in the standing or slowly moving material andgradually increase the run speed setting. When the dryer 1] is returnedto run speed, the speed setting would have been advanced too far foradequate drying of the material that had not yet entered the dryer whileit was standing or operating at low speed. Wet material would, ofcourse, be produced before the control could reduce the speedsufficiently to dry it.

I A- good rule, concerning the start delay timer is to set it to alength of time long enough to permit all dry:

material to reach the dryer exit at the lowest expected operating speed.This should correspond with the heaviest material to bedried.

With the start delay properly set and its time expired after the machinehas begun to operate at normal, run speed, the control will begin tomake speed adjustments depending upon the moisture condition it senses.

If the moisture is normal, which means it is in agreement with theamount set on the set regain selector, no control action will occur.

When the moisture varies from the normal zone, whether the departure istoward dry or wet, the correction delay timer 29 functions. This timer29 which is adjustable from 0 to 60 seconds, determines how long anabnormal condition may exist before the control will act to correct it.It will, for instance, permit temporary wet spots and cut marks on warpsto pass through without causing the control to change speed. Without thecorrection delay, many needless changes, mostly reductions, in speedwill be made, only to require the control to make a compensating changelater, but usually at an accumulating loss in production. This would bethe case if the correction delay timer were set to zero time. On theother hand, if the correction delay timer is set too long, the controlwill be slow to act,

bringing on the likelihood of both overdried (loss in production andquality) and underdried (loss in quality) material. Obviously, somesetting between zero and some excessive length of time should be ideal.There is no specific rule for setting the correction delaypotentiometer; settings found to be best from actual experience are inthe neighborhood of 5 seconds. The general rule is to set the correctiondelay timer long for drying applications in which the moisture is notstable, that is, the moisture variations are constantly causing thecontrol to vary in and out of the normal zone. Such long settings tendto cause the control to stabilize the speed for the preset averagemoisture desired and to make speed changes only as the departures inmoisture from the normal zone tend to become permanent. Conversely, ifthe application is one in which stable and consistent moisture isobtained, there is little justification for any more than a very smallamount of time to be allowed to pass occasional wet spots, cut marks,and the like. The control is then able to make step'by step changes inspeed from time to time to maintain constant moisture at the maximumpossible rate of production.

The correction delay timer 29 then functions each time the moisturebecomes abnormal, and it prevents the control from changing the speeduntil there is reasonable certainty that a change should be made. Themoisture must remain abnormal constantly without even momentarilybecoming normal again until the full time set on the correction delaytimer has expired.

Once a dry or wet condition has proved to be sufficiently permanent tojustify a change in speed, a corresponding speed change is madeinstantly. Separateamount of correction timers determine the amount ofcorrection. The amount of dry correction timer determines the length oftime the control motor 24 will run to increase the speed. The amount ofwet correction timer determines the length of time the control motorwill run to decrease the speed. These timers are ad justable from 0 to 6seconds. The amount of time, is directly related to the change in speedin yards or meters per minute, but this depends upon the response of theparticular drive system, whether electrical or mechanical.

Separate dry and wet correction timers are provided to facilitate makingslightly larger corrections from a wet condition than from a drycondition. Since abnormally wet conditions generally affect materialquality more adversely than abnormally dry conditions, it is possible torun safely at higher average moisture levels by setting the amount ofwet correction timer somewhathigher than the amount of dry correctiontimer. I

The remaining timer 31, frequency of correction, adjustable from 0 to 60seconds, follows after a change in speed has been made. This timer 31will allow a time to elapse so that the change in speed can actuallyinfluence the moisture. If the influence is insufficient to cause themoisture to become normal, a second change in speed will be made, and soon until the abnormal moisture condition is fully corrected.

The two timers, amount of dry correction or amount of wet correction andthe frequency of correction work together in a tandem off-on" manner.Their action stops whenever the moisture returns to normal, after whicha new, abnormal condition must first exist longer than the time set onthe correction delay before another correction will be made.

It would appear that the frequency of correction timer 31 should be setto a time approximately as long as the start delay, since this is verynearly equal the time required for complete travel of the materialthrough the dryer. ln practice, however, this approach does not providethe best performance. After a change is made in the speed, the moisturewill begin to be influenced almost immediately, the full effect beingrealized after full passage of the material through the dryer.Sufficient change in moisture to depart from the normal zone generallyoccurs after about one third the full passage has been made. Since it isdesirable to limit the delay between corrections as much as possible,the frequency of correction timer 31 should be set to about one-thirdthe time required for complete passage. ln actual sizing applicationswhich require a start delay period of 60 seconds, the frequency ofcorrection timer 31 is usually set to 15 to seconds for bestperformance.

With the frequency of correction timer 31 set only long enough to permita departure out of the normal zone upon a given speed change, the twoamount of correction timers should be set to the highest amount possiblewithout excessive hunting. It is not good practice to employ smallamounts of correction simply to avoid overshooting the normal zone. Itis better to allow a tolerable amount of overshoot, provided, of course,the changes are not so great and so often that the control cannot reachequilibrium soon after the corrections are made.

Important advantages of the new moisture control are: I

l. The invention may be calibrated for use on most popular textilefibers being processed throughout the world. All competitive instrumentsthat we are aware of do not offer this advantage. Instead, it isnecessary to make bone dry tests in a laboratory on samples to determinethe actual amount of moisture in the materi- 2. The invention providesmeans for presetting the control to get any desired amount of moisturein material blends as well as in single fiber materials. Tests are madeto determine the relationship between moisture and electrical resistanceof the various popular textile fibers and tables are supplied with theinvention showing such relationships. The Set Regain" selector 48 iscalibrated in units from 3 to 15 which correspond with values ofelectrical resistance. At a setting of 3, the resistance is in theneighborhood of 12,000 megohms. As the selector is rotated toward 15,the resistance decreases to a low of about 12,000 ohms. Since theselector dial 48 is calibrated particularly for cotton, a setting of 7indicates that cotton must contain 7 percent moisture regain for thecontrol to be satisfied under which condition the meter M1 will indicatethe center of the green normal zone. At the same setting rayon must have12.9 percent moisture regain and other fibers will have other moistureregain values which can be determined from tables provided with theinvention. The setting of the Set Regain selector 48 for variousmaterials at specific moisture regain values will be obtained from theproper tables.

in this specification moisture regain is defined as the amount ofmoisture in the material expressed as a percentage of its dryweight,i.e.,

5 Percent moisture regain While the invention has been described inconnection with a specific material condition correcting means (i.e., adryer for correcting the measured moisture condition of web material toconform to a standard moisture condition) it is not intended that theinvention be limited to one specific utility. Various uses andmodifications may become apparent to those skilled in the art to whichthe invention relates. Accordingly, it is not desired to limit theinvention to this disclosure, and various modifications and equivalentsmay be resorted to, falling within the spirit and scope of the inventionas claimed.

What is claimed is:

1. Moisture measuring and control apparatus for use with a materialmoisture conditioning means having conveyor means for conveying thematerial through the material moisture conditioning means and a variablespeed drive means for driving the conveyor means at different speeds asdetermined by said moisture measuring and control apparatus, saidmoisture measuring and control apparatus comprising means forcontinuously measuring the moisture content of material conveyed throughthe material moisture conditioning means and producing an electricaloutput signal related to the moisture in the material, a control pointselector means for generating a reference signal related to a selectedstandard moisture content, a control comparator means for comparing themeasured moisture signal with the reference signal, said controlcomparator means generating a wet condition signal when said measuredmoisture content exceeds the standard moisture content by apredetermined amount, generat- 1 ing a dry condition signal when themeasured moisture content is less than the standard moisture content bya predetermined amount and generating a normalsignal when the -measuredmoisture content is within a predetermined range centered with respectto said standard moisture content, means "responsive to said drycondition signal for producing dry correction control signals, meansresponsive to said wet condition signal for producing-wet correctioncontrol signals,

means responsive alternatively to said dry and wet correction controlsignals for increasing and decreasing respectively the speed of saidvariable speed conveyor drive means, and timing means for permittingsaid means for producing dry correction control signals to respond tosaid dry condition signals and for permitting said means for producingwet correction control signals to respond to said wet condition signalsonly during periods of predetermined time duration at reoccurringintervals of predetermined frequency while said dry and wet conditionsignals continue, said timing means including an amount of correctiontimer means which determines the length of the time periods during whichthe dry and wet condition signals may be applied to said means forproducing dry correction control signals and to said means for producingwet correction control signals respectively, and a frequency ofcorrection timer means for periodically resetting said amount ofcorrection timer at a predetermined frequency.

2. The apparatus set forth in claim 1 wherein said time delay periodincludes a start time delay initiated when the material conveying meansbegins to move material through the material moisture conditioning meansand a correction time delay initiated at the end of said start timedelay and only when said comparator is generating a dry or wet conditionsignal.

3. The apparatus set forth in claim 1 wherein said moisture measuringmeans is an electrical resistance type moisture meter which includes asubstantially constant d.c. voltage source, a pair of electrodes forcontinuously bridging a portion of the material to be measured and a setmoisture control resistor in series circuit with said voltage source andsaid electrodes, said set moisture control resistor being adjustable andbeing normally set so that its resistance value is equivalent to theresistance of the material to be measured at the desired moisture level,high input impedance voltage to current converter means for sensing thevoltage across the set moisture resistor and producing an output currentwhich is directly proportional to the voltage drop across the setmoisture control resistor, a current to voltage converter responsive tosaid output current from said voltage to current converter forconverting and scaling said output current into a ground-referredvoltage, a moisture indicator means responsive to said ground-referredvoltage for indicating the moisture content of said material, andcircuit means for applying said ground-referred voltage to said controlcomparator.

4. The apparatus set forth in claim 3 wherein said moisture indicatorhas an indicator dial including a central normal zone, a wet zone and adry zone, said wet zone and dry zone being on opposite sides of saidnormal zone.

5. Moisture measuring and control apparatus for use with a materialmoisture conditioning means having conveyor means for conveying thematerial through the material moisture conditioning means and a variablespeed drive means for driving the conveyor means at different speeds asdetermined by said moisture measuring and control apparatus, saidmoisture measuring and control apparatus comprising means forcontinuously measuring the moisture content of material conveyed throughthe material moisture conditioning means and producing an electricaloutput signal related to the moisture in the material, a control pointselector means for generating a reference signal related to a selectedstandard moisture content, a control comparator means for comparing themeasured moisture signal with the reference signal, said controlcomparator means generating a wet condition signal when said measuredmoisture content exceeds the standard moisture content by apredetermined amount, generating a dry condition signal when themeasured moisture content is less than the standard moisture content bya predetermined amount and generating a normal signal when the measuredmoisture content is within a predetermined range centered with respectto said standard moisture content, means responsive to said drycondition signal for producing dry correction control signals, meansresponsive to said wet condition signal for producing wet correctioncontrol signals,

means responsive alternatively to said dry and wet correction controlsignals for increasing and decreasing respectively the speed of saidvariable speed conveyor drive means, and timing means for permittingsaid means for producing dry correction control signals to respond tosaid dry condition signals and for permitting said means for producingwet correction control signals to respond to said wet condition signalsonly during periods of predetermined time duration at reoccurringintervals of predetermined frequency while said dry and wet conditionsignals continue and only after a time delay period, said moisturemeansuring means being an electrical resistance type moisture meterwhich includes a substantially constant d.c. voltage source, a pair ofelectrodes for continuously bridging a portion of the material to bemeasured and a set moisture control resistor in series circuit with saidvoltage source and said electrodes, said set moisture control resistorbeing adjustable and being normally set so that its resistance value isequivalent to the resistance of the material to be measured at thedesired moisture level, high input impedance voltage to currentconverter means for sensing the voltage across the set moisture resistorand producing an output current which is directly proportional to thevoltage drop across the set moisture control resistor, a current tovoltage converter responsive to said output current from said voltage tocurrent converter for converting and scaling said output current into aground-referred voltage, a moisture indicator means responsive to saidground-referred voltage for indicating the moisture content of saidmaterial, and circuit means for applying said ground-referred voltage tosaid control comparator, said moisture indicator having an indicatordial including a central normal zone, a wet zone and a dry zone, saidwet zone and dry zone being on opposite sides of said normal zone, andsaid control comparator consisting of two operational amplifiersoperating open loop for maximum sensitivity, each operational amplifierhaving an inverting input, a non-inverting input and an output terminal,one operational amplifier having its non-inverting input connected toreceive the output voltage from said current to voltage converterwhilethe other operational amplifier has its inverting input connected toreceive the output voltage from said current to voltage converter, theone operational amplifier having its inverting input connected toreceive said reference signal from said control point selector and theother operational amplifier having its non-inverting input connected toreceive said reference signal from said control point selector, and acontrol sensitivity adjusting means for said comparator whereby theoperational amplifiers are caused to produce said normal output signalwhen the moisture indicator reads within said normal zone.

6. The apparatus set forth in claim 5 wherein said means responsive tosaid dry condition signal for producing dry correction control signalsincludes a normally open, dry condition signal responsive switch inseries circuit with a voltage source and the energizing coil of a drycorrection relay, and wherein said means responsive to said wetcondition signal for producing wet correction control signals includes anormally open wet condition signal responsive switch in series circuitwith a voltage source and the energizing coil of a wet correction relay.

7. The apparatus set forth in claim 6 wherein said normally open drycondition signal responsive switch and said normally open wet conditionsignal responsive switch are solid state switches which are normallybiased to cut off.

8. The apparatus set forth in claim 6 wherein said timing means providesbias for maintaining said normally open dry condition signal responsiveswitch and said normally open wet condition signal responsive switchopen even when dry and wet condition signals are present, and removessaid bias for periods of predetermined time duration at reoccurringintervals of predetermined frequency while saiddry and wet conditionsignals continue thus permitting said dry and wet condition signalresponsive switches to respond to said dry and wet condition signalsrespectively while said bias is removed.

9. The apparatus set forth in claim 6 wherein said means alternativelyresponsive to said dry and wet correction control signals includes areversible correction control motor, a speed control potentiometerdriven by said reversible correction control motor for adjusting thespeed of said variable speed conveyor drive, and reversing circuit meansfor energizing said reversible correction control motor selectively inopposite directions, said reversing circuit means being controlled bysaid dry correction relay when energized to cause said correctioncontrol motor to move said speed control potentiometer in a direction toincrease the speed of said variable speed conveyor drive means and saidreversing circuit means being controlled by said wet correction relaywhen energized to cause said correction control motor to move said speedcontrol potentiometer in a direction to decrease the speed of saidvariable speed conveyor drive means.

10. Moisture measuring and control apparatus for use with a materialmoisture conditioning means having conveyor means for conveying thematerial through the material moisture conditioning means and a variablespeed drive means for driving the conveyor means at different speeds asdetermined by said moisture measuring and control apparatus, saidmoisture measuring and control apparatus comprising means forcontinuously measuring the moisture content of material conveyed throughthe material moisture conditioning means and producing an electricaloutput signal related to the moisture in the material, a control point,selector means for generating a reference signal related to a selectedstandard moisture content, a control comparator means for comparing themeasured moisture signal with the reference signal, said controlcomparator means generating a wet condition signal when said measuredmoisture content exceeds the standard moisture content by apredetermined amount, generating a dry condition signal when themeasured moisture content is less than the standard moisture content bya predetermined amount and generating a normal signal when the measuredmoisture content is within a predetermined range centered with respectto said standard moisture content, means responsive to said drycondition signal for producing dry correction control signals, meansresponsive to said wet condition signal for producing wet correctioncontrol signals, means responsive alternatively to said dry and wetcorrection control signals for increasing and decreasing respectivelythe speed of said variable speed conveyor drive means and timing meansfor blocking said dry and wet condition signals from said means forproducing dry correction control signals and said means for producingwet correction control signals respectively and for unblocking said dryand wet condition signals during time periods of predetermined length atreocurring intervals, said timing meansincluding an amount of correctiontimer means which determines the length of the time periods during whichthe' dry and wet condition signals are applied to said means forproducing dry correction control signals and to said means for producingwet correction control signals respectively, and a frequency ofcorrection timer means for periodically resetting said amount ofcorrection timer at a predetermined frequency.

11. The apparatus set forth in claim 10 wherein said amount ofcorrection timer means includes an amount of dry correction timer meansfor unblocking the means for producing dry correction signals and anamount of wet correction timer means for unblocking the means forproducing wet correction signals, and means for selecting the amount ofdry correction timer means to operate only when a dry condition signalis being generated, and for selecting the amount of wet correction timermeans to operate when said wet condition signal is being generated.

12. The apparatus set forth in claim 11 wherein said amount of drycorrection timer means and said amount of wet correction timer means areadjustable for operating over time periods of different length.

13. The apparatus setforth in claim 12 wherein said amount of wetcorrection timer means isadjusted to operate over a longer time periodthan said amount of dry correction timer means.

14.'The apparatus set forth in claim 13 wherein said timing meansfurther includes a correction delay timer means for delaying theoperation of said amount of correction timer means a predetermined timeperiod after said comparator begins to generate wet or dry conditionsignals to assure that an abnormal signal persists long enough towarrant correction.

15. The apparatus set forth in claim 14 wherein said timing meansfurther includes a start delay timer means for delaying the operation ofsaid correction delay timer fora predetermined time period after thematenial conveying means begins to move material through the materialm'oisture conditioning means.

l6. Moisture measuring and control apparatus for use with a materialmoisture conditioning means having conveyor means for conveying thematerial through the material moisture conditioning means and a variablespeed drive means for drivingthe conveyor means at different speeds asdetermined by said moisture measuring and control apparatus, saidmoisture measuring and control apparatus comprising means forcontinuously measuring the moisture content of material conveyed throughthe material moisture conditioning means and producing an electricaloutput signal related to the moisture in the material, a control pointselector means for generating a reference signal related to a selectedstandard moisture content, a control comparator means'for comparing themeasured moisture signal with the reference signal, said controlcomparator means generating a wet condition signal when said measuredmoisture. content exceeds the standard moisture content by apredetermined amount, generating a dry condition signal when themeasured moisture content is less than the standard moisture content bya predetermined amount and generating a normal signal when the measuredmoisture content is within a predetermined range centered with respectto said standard moisture content, means responsive to said drycondition signal for producing dry correction control signals, meansresponsive to said wet condition signal for producing wet correctioncontrol signals, means responsive alternatively to said dry and wetcorrection control signals for increasing and decreasing respectivelythe speed of said variable speed conveyor drive means and timing meansfor blocking said dry and wet condition signals from said means forproducing dry correction control signals and said means for producingwet correction control signals respectively and for unblocking said dryand wet condition signals during time periods of predetermined length atreoccuring intervals, said timing means including a start delay timerfor establishing a start time delay sufficient to permit the material inthe conditioning means at the time it is started to clear the machine, acorrection delay timer which establishes a time delay period after thestart time delay which insures that a condition requiring correctionpersists long enough to warrant correction, an amount of correctiontimer which is actuated after the correction delay period to establish atime period during which time said means responsive to said wet and drycondition signals for producing wet and dry correction control signalsrespectively are unblocked and permitted to respond to said wet and drycondition signals respectively, and a frequency of correction timerwhich is actuated at the end of the time period established by theamount of correction timer to recycle the amount of correction timer atreoccurring intervals of predetermined frequency for as long as anabnormal condition signal is being generated.

17. The apparatus set forth in claim 16 wherein said timers areenergized from the same power source, and sequencing means are providedfor energizing said start delay timer when the conditioning means isturned on, for energizing said correction delay timer after the startdelay period and when an abnormal condition signal is being generated,for energizing said amount of correction timer at the end of saidcorrection time delay, for energizing said frequency of correction timerat the end of the time period established by the amount of correctiontimer.

18. The apparatus set forth in claim 17 wherein said sequencing meansincludes a plurality of series switches separating the respective timersfrom said power source, said series switches including a first normallyopen switch connected in a sequencing circuit between said power sourceand said start delay timer which is closed when said moistureconditioning means is turned on, a second normally open switch connectedin said sequencing circuit between said start delay timer and saidcorrection delay timer which is closed at the end of said start delaywhen an abnormal condition signal is being generated, a third normallyopen switch connected in said sequencing circuit between said correctiondelay timer and said amount of correction timer which is closed at theend of said correction delay period, and a fourt h normally open switchconnected in said sequencing circuit between said amount of correctiontimer and said frequency of correction timer which is closed at the endof said amount of correction time period.

19. The apparatus set forth in claim 18 wherein said switches are solidstate switches and said timers are solid state timers.

20. The apparatus set forth in claim 16 wherein all of said timers havemeans for adjusting their respective time periods.

1. Moisture measuring and control apparatus for use with a materialmoisture conditioning means having conveyor means for conveying thematerial through the material moisture conditioning means and a variablespeed drive means for driving the conveyor means at different speeds asdetermined by said moisture measuring and control apparatus, saidmoisture measuring and control apparatus comprising means forcontinuously measuring the moisture content of material conveyed throughthe material moisture conditioning means and producing an electricaloutput signal related to the moisture in the material, a control pointselector means for generating a reference signal related to a selectedstandard moisture content, a control comparator means for comparing themeasured moisture signal with the reference signal, said controlcomparator means generating a wet condition signal when said measuredmoisture content exceeds the standard moisture content by apredetermined amount, generating a dry condition signal when themeasured moisture content is less than the standard moisture content bya predetermined amount and generating a normal signal when the measuredmoisture content is within a predetermined range centered with respectto said standard moisture content, means responsive to said drycondition signal for producing dry correction control signals, meansresponsive to said wet condition signal for producing wet correctioncontrol signals, means responsive alternatively to said dry and wetcorrection control signals for increasing and decreasing respectivelythe speed of said variable speed conveyor drive means, and timing meansfor permitting said means for producing dry correction control signalsto respond to said dry condition signals and for permitting said meansfor producing wet correction control signals to respond to said wetcondition signals only during periods of predetermined time duration atreoccurring intervals of predetermined frequency while said dry and wetcondition signals continue, said timing means including an amount ofcorrection timer means which determines the length of the time periodsduring which the dry and wet condition signals may be applied to saidmeans for producing dry correction control signals and to said means forproducing wet correction control signals respectively, and a frequencyof correction timer means for periodically resetting said amount ofcorrection timer at a predetermined frequency.
 2. The apparatus setforth in claim 1 wherein said time delay period includes a start timedelay initiated when the material conveying means begins to movematerial through the material moisture conditioning means and acorrection time delay initiated at the end of said start time delay andonly when said comparator is generating a dry or wet condition signal.3. The apparatus set forth in claim 1 wherein said moisture measuringmeans is an electrical resistance type moisture meter which includes asubstantially constant d.c. voltage source, a pair of electrodes forcontinuously bridging a portion of the material to be measured and a setmoisture control resistor in series circuit with said voltage source andsaid electrodes, said set moisture control resistor being adjustable andbeing normally set so that its resistance value is equivalent to theresistance of the material to be measured at the desired moisture level,high input impedance voltage to current converter means for sensing thevoltage across the set moisture resistor and producing an output currentwhich is directly proportional to the voltage drop across the setmoisture control resistor, a current to voltage converter responsive tosaid output current from said voltage to current converter forconverting and scaling said output current into a ground-referredvoltage, a moisture indicator means responsive to said ground-referredvoltage for indicating the moisture content of said material, andcircuit means for applying said ground-referred voltage to said controlcomparator.
 4. The apparatus set forth in claim 3 wherein said moistureindicator has an indicator dial including a central normal zone, a wetzone and a dry zone, said wet zone and dry zone being on opposite sidesof said normal zone.
 5. Moisture measuring and control apparatus for usewith a material moisture conditioning means having conveyor means forconveying the material through the material moisture conditioning meansand a variable speed drive means for driving the conveyor means atdifferent speeds as determined by said moisture measuring and controlapparatus, said moisture measuring and control apparatus comprisingmeans for continuously measuring the moisture content of materialconveyed through the material moisture conditioning means and producingan electrical output signal related to the moisture in the material, acontrol point selector means for generating a reference signal relatedto a selected standard moisture content, a control comparator means forcomparing the measured moisture signal with the reference signal, saidcontrol comparator means generating a wet condition signal when saidmeasured moisture content exceeds the staNdard moisture content by apredetermined amount, generating a dry condition signal when themeasured moisture content is less than the standard moisture content bya predetermined amount and generating a normal signal when the measuredmoisture content is within a predetermined range centered with respectto said standard moisture content, means responsive to said drycondition signal for producing dry correction control signals, meansresponsive to said wet condition signal for producing wet correctioncontrol signals, means responsive alternatively to said dry and wetcorrection control signals for increasing and decreasing respectivelythe speed of said variable speed conveyor drive means, and timing meansfor permitting said means for producing dry correction control signalsto respond to said dry condition signals and for permitting said meansfor producing wet correction control signals to respond to said wetcondition signals only during periods of predetermined time duration atreoccurring intervals of predetermined frequency while said dry and wetcondition signals continue and only after a time delay period, saidmoisture meansuring means being an electrical resistance type moisturemeter which includes a substantially constant d.c. voltage source, apair of electrodes for continuously bridging a portion of the materialto be measured and a set moisture control resistor in series circuitwith said voltage source and said electrodes, said set moisture controlresistor being adjustable and being normally set so that its resistancevalue is equivalent to the resistance of the material to be measured atthe desired moisture level, high input impedance voltage to currentconverter means for sensing the voltage across the set moisture resistorand producing an output current which is directly proportional to thevoltage drop across the set moisture control resistor, a current tovoltage converter responsive to said output current from said voltage tocurrent converter for converting and scaling said output current into aground-referred voltage, a moisture indicator means responsive to saidground-referred voltage for indicating the moisture content of saidmaterial, and circuit means for applying said ground-referred voltage tosaid control comparator, said moisture indicator having an indicatordial including a central normal zone, a wet zone and a dry zone, saidwet zone and dry zone being on opposite sides of said normal zone, andsaid control comparator consisting of two operational amplifiersoperating open loop for maximum sensitivity, each operational amplifierhaving an inverting input, a non-inverting input and an output terminal,one operational amplifier having its non-inverting input connected toreceive the output voltage from said current to voltage converter whilethe other operational amplifier has its inverting input connected toreceive the output voltage from said current to voltage converter, theone operational amplifier having its inverting input connected toreceive said reference signal from said control point selector and theother operational amplifier having its non-inverting input connected toreceive said reference signal from said control point selector, and acontrol sensitivity adjusting means for said comparator whereby theoperational amplifiers are caused to produce said normal output signalwhen the moisture indicator reads within said normal zone.
 6. Theapparatus set forth in claim 5 wherein said means responsive to said drycondition signal for producing dry correction control signals includes anormally open, dry condition signal responsive switch in series circuitwith a voltage source and the energizing coil of a dry correction relay,and wherein said means responsive to said wet condition signal forproducing wet correction control signals includes a normally open wetcondition signal responsive switch in series circuit with a voltagesource and the energizing coil of a wet correction relay.
 7. Theapparatus set forth in claim 6 wherein said normally open dry conditionsignal responsive switch and said normally open wet condition signalresponsive switch are solid state switches which are normally biased tocut off.
 8. The apparatus set forth in claim 6 wherein said timing meansprovides bias for maintaining said normally open dry condition signalresponsive switch and said normally open wet condition signal responsiveswitch open even when dry and wet condition signals are present, andremoves said bias for periods of predetermined time duration atreoccurring intervals of predetermined frequency while said dry and wetcondition signals continue thus permitting said dry and wet conditionsignal responsive switches to respond to said dry and wet conditionsignals respectively while said bias is removed.
 9. The apparatus setforth in claim 6 wherein said means alternatively responsive to said dryand wet correction control signals includes a reversible correctioncontrol motor, a speed control potentiometer driven by said reversiblecorrection control motor for adjusting the speed of said variable speedconveyor drive, and reversing circuit means for energizing saidreversible correction control motor selectively in opposite directions,said reversing circuit means being controlled by said dry correctionrelay when energized to cause said correction control motor to move saidspeed control potentiometer in a direction to increase the speed of saidvariable speed conveyor drive means and said reversing circuit meansbeing controlled by said wet correction relay when energized to causesaid correction control motor to move said speed control potentiometerin a direction to decrease the speed of said variable speed conveyordrive means.
 10. Moisture measuring and control apparatus for use with amaterial moisture conditioning means having conveyor means for conveyingthe material through the material moisture conditioning means and avariable speed drive means for driving the conveyor means at differentspeeds as determined by said moisture measuring and control apparatus,said moisture measuring and control apparatus comprising means forcontinuously measuring the moisture content of material conveyed throughthe material moisture conditioning means and producing an electricaloutput signal related to the moisture in the material, a control pointselector means for generating a reference signal related to a selectedstandard moisture content, a control comparator means for comparing themeasured moisture signal with the reference signal, said controlcomparator means generating a wet condition signal when said measuredmoisture content exceeds the standard moisture content by apredetermined amount, generating a dry condition signal when themeasured moisture content is less than the standard moisture content bya predetermined amount and generating a normal signal when the measuredmoisture content is within a predetermined range centered with respectto said standard moisture content, means responsive to said drycondition signal for producing dry correction control signals, meansresponsive to said wet condition signal for producing wet correctioncontrol signals, means responsive alternatively to said dry and wetcorrection control signals for increasing and decreasing respectivelythe speed of said variable speed conveyor drive means and timing meansfor blocking said dry and wet condition signals from said means forproducing dry correction control signals and said means for producingwet correction control signals respectively and for unblocking said dryand wet condition signals during time periods of predetermined length atreocurring intervals, said timing means including an amount ofcorrection timer means which determines the length of the time periodsduring which the dry and wet condition signals are applied to said meansfor producing dry correction control signals and to said means forproducing wet correction control signals respectively, and a frequencyof correction timer means for periodically resetting said amount ofcorrection timer at a predetermined frequency.
 11. The apparatus setforth in claim 10 wherein said amount of correction timer means includesan amount of dry correction timer means for unblocking the means forproducing dry correction signals and an amount of wet correction timermeans for unblocking the means for producing wet correction signals, andmeans for selecting the amount of dry correction timer means to operateonly when a dry condition signal is being generated, and for selectingthe amount of wet correction timer means to operate when said wetcondition signal is being generated.
 12. The apparatus set forth inclaim 11 wherein said amount of dry correction timer means and saidamount of wet correction timer means are adjustable for operating overtime periods of different length.
 13. The apparatus set forth in claim12 wherein said amount of wet correction timer means is adjusted tooperate over a longer time period than said amount of dry correctiontimer means.
 14. The apparatus set forth in claim 13 wherein said timingmeans further includes a correction delay timer means for delaying theoperation of said amount of correction timer means a predetermined timeperiod after said comparator begins to generate wet or dry conditionsignals to assure that an abnormal signal persists long enough towarrant correction.
 15. The apparatus set forth in claim 14 wherein saidtiming means further includes a start delay timer means for delaying theoperation of said correction delay timer for a predetermined time periodafter the material conveying means begins to move material through thematerial moisture conditioning means.
 16. Moisture measuring and controlapparatus for use with a material moisture conditioning means havingconveyor means for conveying the material through the material moistureconditioning means and a variable speed drive means for driving theconveyor means at different speeds as determined by said moisturemeasuring and control apparatus, said moisture measuring and controlapparatus comprising means for continuously measuring the moisturecontent of material conveyed through the material moisture conditioningmeans and producing an electrical output signal related to the moisturein the material, a control point selector means for generating areference signal related to a selected standard moisture content, acontrol comparator means for comparing the measured moisture signal withthe reference signal, said control comparator means generating a wetcondition signal when said measured moisture content exceeds thestandard moisture content by a predetermined amount, generating a drycondition signal when the measured moisture content is less than thestandard moisture content by a predetermined amount and generating anormal signal when the measured moisture content is within apredetermined range centered with respect to said standard moisturecontent, means responsive to said dry condition signal for producing drycorrection control signals, means responsive to said wet conditionsignal for producing wet correction control signals, means responsivealternatively to said dry and wet correction control signals forincreasing and decreasing respectively the speed of said variable speedconveyor drive means and timing means for blocking said dry and wetcondition signals from said means for producing dry correction controlsignals and said means for producing wet correction control signalsrespectively and for unblocking said dry and wet condition signalsduring time periods of predetermined length at reoccuring intervals,said timing means including a start delay timer for establishing a starttime delay sufficient to permit the material in the conditioning meansat the time it is started to clear the machine, a correction delay timerwhich establishes a time delay period after the start time delay whichinsures that a condition requiring correction persists long enough towarrant correction, an amount of correction timer which is actuatedafter the correction delay period to establish a time period duringwhich time said means responsive to said wet and dry condition signalsfor producing wet and dry correction control signals respectively areunblocked and permitted to respond to said wet and dry condition signalsrespectively, and a frequency of correction timer which is actuated atthe end of the time period established by the amount of correction timerto recycle the amount of correction timer at reoccurring intervals ofpredetermined frequency for as long as an abnormal condition signal isbeing generated.
 17. The apparatus set forth in claim 16 wherein saidtimers are energized from the same power source, and sequencing meansare provided for energizing said start delay timer when the conditioningmeans is turned on, for energizing said correction delay timer after thestart delay period and when an abnormal condition signal is beinggenerated, for energizing said amount of correction timer at the end ofsaid correction time delay, for energizing said frequency of correctiontimer at the end of the time period established by the amount ofcorrection timer.
 18. The apparatus set forth in claim 17 wherein saidsequencing means includes a plurality of series switches separating therespective timers from said power source, said series switches includinga first normally open switch connected in a sequencing circuit betweensaid power source and said start delay timer which is closed when saidmoisture conditioning means is turned on, a second normally open switchconnected in said sequencing circuit between said start delay timer andsaid correction delay timer which is closed at the end of said startdelay when an abnormal condition signal is being generated, a thirdnormally open switch connected in said sequencing circuit between saidcorrection delay timer and said amount of correction timer which isclosed at the end of said correction delay period, and a fourth normallyopen switch connected in said sequencing circuit between said amount ofcorrection timer and said frequency of correction timer which is closedat the end of said amount of correction time period.
 19. The apparatusset forth in claim 18 wherein said switches are solid state switches andsaid timers are solid state timers.
 20. The apparatus set forth in claim16 wherein all of said timers have means for adjusting their respectivetime periods.